Papillomaviruses (PV) are members of the papovavirus family and contain a double stranded circular DNA genome with a typical size of about 7900 base pairs (bp). Human papillomaviruses (HPV) are recognized as a cause of various epithelial lesions such as warts, condylomas and dysplasias. See, Gissman, L., Cancer Survey, 3:161 (1984); Boshart et al, ENBO J., 3:1151 (1984); Romanczuk et al, J. Virol., 65:2739-2744 (1991); Jenson et al, In "Papillomaviruses and human cancer" (H. Pfister. Ed.), pp. 11-43, CRC Press (1990); Schlegel, R., "Papillomaviruses and human cancer" In: Viral pathogenesis (ed. Fujinami, R.), Seminars in Virology 1:297-306 (1990); and Jenson et al, "Human Papillomaviruses" In Belshe, R. ed. Textbook of human virology, Second Edition: MASS:PSG, 1989:951.
HPVs are grouped into types based on the similarity of their DNA sequence. Two HPVs are taxonomically classified as being of the same type if their DNAs cross-hybridize to greater than 50% as measured by hybridization in solution under moderately stringent hybridization conditions.
A number of distinct papillomaviruses have been shown to infect humans. Papillomaviruses are highly species and tissue-specific, and are characterized by a specific mode of interaction with the squamous epithelia they infect. These small DNA tumor viruses colonize various stratified epithelia like skin and oral and genital mucosa, and induce the formation of self-limiting benign tumors known as papillomas (warts) or condylomas. These tumors are believed to arise from an initial event in the infectious cycle where the virus enhances the division rate of the infected stem cell in the epithelial basal layer, before it is replicated in the differentiating keratinocyte.
The term papillomavirus covers a large number of viruses which are considered responsible for several forms of viral infection ranging from relatively benign warts of the skin or mucous membranes to hyperplasias susceptible to progressing into dysplasias or intra-epithelial neoplasms, and malignant conversion to various forms of cancer, the most significant being that of the female uterine cervix.
A number of HPVs types have been identified. Furthermore, the preferential association of certain HPV types with anatomic location and distinct types of lesions gives support to the hypothesis that different HPV-induced lesions constitute distinct diseases, and that the clinical patterns of lesions express specific biological properties of distinct types of HPVs. Distinctive histological features have been associated with the infection of the skin or mucous membranes by different types of HPVs.
The genomes of different HPV types have been cloned and characterized. In particular, the genomes of two HPV types, HPV 16 and HPV 18, have been found to be associated with about 70% of invasive carcinomas of the uterine cervix.
Human papillomaviruses which infect the genital tract mucosa play a critical role in the development of cervical cancer. See, Lorincz et al, Obstetrics & Gynecology, 79:328-337 (1992); Beaudenon et al, Nature, 321:246-249 (1986); and Holloway et al, Gynecol. Onc., 41:123-128 (1991). For example, the majority of humans cervical carcinomas (95%) contain and express HPV DNA and it is the expression of two viral oncoproteins, E6 and E7, which appears to be critical for cellular transformation and maintenance of the transformed state. Despite the detailed knowledge concerning the molecular mechanism of action of these oncoproteins, there is little information available on the biology of papillomavirus infection, including the identity of viral receptors, the control of viral replication and assembly, and the host immune response to virus and virally-transformed cells. An effective vaccine against HPV infection could potentially reduce the incidence of human cervical dysplasia and carcinoma by 90-95%. However, there is no tissue culture system which permits sufficient keratinocyte differentiation to propagate the PV in-vitro. Because of the widespread occurrence of HPV infection, methods for detecting, preventing and treating viral infection are needed. Also, methods for detecting, preventing and treating papillomavirus infection in animals, e.g., equines and canines, are also needed.
Canine papillomas were one of the first animal systems studied when McFaydean and Hobday transmitted the oral papilloma in 1898. Today, dogs are commonly used as models for a variety of diseases and much is known about their physiology and immune system. Papillomas affect many anatomic locations in dogs, similar to the human diseases. Puppies may have marginal papillae on their tongues which are normal anatomic structures resembling oral papillomas. True papillomas can be found on the dorsal tongue and buccal mucosa, ocular mucous membranes, mucous membranes of the lower genital tracts of both males and females, and haired skin. The lesions are characterized by epithelial proliferation on thin fibrovascular stalks and there may be specific cytopathic effects in the stratum granulosum in which the cells swell, develop large keratohyalin-like granules, and may have intranuclear inclusions. Group-specific papillomavirus antigens can be detected by the cells exhibiting cytopathic effects.
The canine oral papillomavirus has been cloned and characterized (Sundberg et al, Amer. J. Vet. Res., 47(5), 1142-1177 (1986)). The COPV viral genome was cloned into pBR322, a restriction map constructed, with the completeness of the COPV genome confirmed by comparison of restriction fragment sizes derived from cloned and virion DNA. (Id.) It is known that COPV is antigenically similar to other papillomaviruses. For example, it has been reported that some of the antigenic and immunogenic epitopes of HPV16 and bovine, canine and avian papillomaviruses are shared. (Dillner et al, J. Virol., 65(12), 5862-6871, (1991)).
Strong evidence suggests that canine papillomaviruses play a role in squamous cell carcinoma development. For example, papillomavirus antigens are detected in penile and vulvar carcinomas. Also, it has been reported that intramuscular injection of canine oral papillomavirus results in the later development of cutaneous squamous cell carcinoma.
Papillomas are also prevalent in equines. In fact, papillomas are probably the most common equine tumor; however, few are ever submitted to diagnostic laboratories for histologic confirmation. Papillomas in equines generally affect the skin, mouth, lower genital tract and eyes. Papillomavirus which causes infection in equines is of the cutaneous type. Equine papillomaviruses have also been isolated and cloned. It is also known that equine papillomavirus infection causes millions of dollars in losses annually to the equine industry. Thus, based on the foregoing, it is clear that there exists a need for effective vaccines against papillomaviruses including HPV's and animal papillomaviruses such as COPV and equine papillomavirus.